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Bolt and probe design....what dimensions?

May 6 2012 at 6:20 PM

  (Login Stealth_Warrior)
Crosman Forum Member
from IP address 99.73.32.170

Alright guys this isn't really gun or caliber specific. But I thought I'd ask yall since alot of your create .20 and .25s and the factory bolt won't work. What's the basic theory in designing a bolt for say a 22xx gun. I'm interested in possibily throwing a LW .20 cal barrel on a Disco, it's current bolt is for a .22 caliber so I'm assuming this will be too big. I recognize that the oring helps seal air from escaping from the bolt, but how much smaller from the barrel ID should the bolt body be? Looking for some guidance or any opinons. Thanks guys.

Semper Fi,
Derek

 
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(Login bloodypheniox)
Crosman Forum Member
174.252.48.216

i just had this problem

May 6 2012, 6:33 PM 

I put a 24" lw barrel on my 2300s with a long steel breech(which essentially has the same dimensions as a disco breech) I couldn't find a bolt small enough to push the pellet all the way in. I could hold the bolt foward and it would seal right at the end of the barrel but I couldn't get the bolt handle all the way foward in the breech, so what I did was just grind down the bolt behind the seal so that it would push farther into the barrel. Also make sure your lw barrel has a lead in/chamfer at the end or loading pellets will be your worst nightmare. And to answer your original question the bolt id won't matter as long as you can get a good seal from that o-ring. Hoped that helped a little.

 
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(Login Stealth_Warrior)
Crosman Forum Member
99.73.32.170

Hmm I wonder if it'd be easier to....

May 6 2012, 7:34 PM 

Put the O-ring in the barrel with a groove like the Marauder .25 barrels or to incorpate the seal with the bolt. Thanks for the chamfer tip. We do the same thing at school for fire arm barrels so the edge won't make a burr on the case or prevent extraction.

 
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Phil
(Login Duane30)
Crosman Forum Member
74.140.196.166

.17 bolt for .20cal; .22 bolt for .25cal works...

May 6 2012, 7:32 PM 

To turn down the bolt tip to work, without a lathe, chuck the bolt into a drill and get out some files. Do not grind away a the o-ring area, it isn't needed. To use a .17 bolt for a .20 barrel, you need a larger o-ring is all. Same for a .22 bolt used with a .25cal barrel, without the need of turning down the bolt to fit the barrel.

All of the current bolts from Crosman (22XX and Disco series) are the same diameter. The only difference being the probe end.

"The majority of things in our lives are created by folks no smarter than the rest. Afterall, the world is comprised, and operated by C average people intellctually, academically, and morally. These people are often the great pioneers that set the precedent for what excellence should be."

 
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(Login Stealth_Warrior)
Crosman Forum Member
99.73.32.170

thanks Phil, exactly what I was looking for....

May 6 2012, 7:38 PM 

I have a lathe so turning down the current bolt shouldn't be a problem. I reckon I'll have to get a small o-ring kit and just do a trial and error. Is it better for the probe to push from inside the skirt, or would a larger probe that pushes the entire pellet work more efficently?

 
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Phil
(Login Duane30)
Crosman Forum Member
74.140.196.166

Probe pushing pellet...

May 6 2012, 9:34 PM 

With lager calibers (for me, above .22cal) a probe that pushes from the skirt (a blow through probe) is a nice feature. For .17 and .22 I find that a blow through probe doesn't do much, if anything at all in the way of performance. Reason being, the port on the probe is very small and possibly restricts more flow than promotes it. On larger calibers, sure, it is fantastic. The larger diameter rounds, thus barrel and probe, give a great deal more room for blow through designs.

Also, if the leade in is done properly (factory does it), i.e. with a lathe, a single probe barb (conventional design) works very well, if not the best for the small calibers. Where the magic comes form on the small calibers is the diamter and length of the probe itself. Not knocking Crosman, but their probe ends fall a a bit short - big time. For example, remove the breech and barrel and have them mated up along with the bolt. Look through the bottom of the transfer hole as you close the bolt home. You will see that often (pellet choice) the pellet skirt is partially over the trasfer hole. This is not good and reduces flow and velocity.

With a traditional probe, center pushing, most pellets load properly because they are longer than they are in diameter. They self align unless the leade in is out of whack.

You can take a Crosman bolt and center drill a small hole in the probe face then insert a small piece of music wire as an extended probe.

"The majority of things in our lives are created by folks no smarter than the rest. Afterall, the world is comprised, and operated by C average people intellctually, academically, and morally. These people are often the great pioneers that set the precedent for what excellence should be."


    
This message has been edited by Duane30 from IP address 74.140.196.166 on May 6, 2012 11:06 PM


 
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(Login bigbore)
Crosman Forum Member
108.132.151.178

I made an extended probe...

May 6 2012, 10:22 PM 

using a drill bit and a drill press. I didn't have a lathe at the time so it's a little off center but it works fine. I forget which size bit I used but after I drilled the hole, I cut the smooth end off the bit and used it for the probe.

Notice that I cut the original probe off just in front of the O-ring groove. The longer probes make assembly a little more difficult. A little too long, impossible to access the 4-40 screw if it's in the new rear position.

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This message has been edited by bigbore from IP address 108.132.151.178 on May 6, 2012 10:25 PM


 
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(Login curt44319)
Crosman Forum Member
66.181.110.200

For me,

May 12 2012, 4:33 PM 

I fail to see any good reason for any particular dimension, AS LONG AS the breech is sealed, and
the difference isn't so much as to cause excessive wear on the "O" ring.
Recently, I turned down the ridge on the pellet side of a .22 bolt slightly to fit into
a .177 breech enough for the .22 "O" ring to seal the .177 barrel.
Working great, on both calibers.

Being a destructive sort, I also super glued a piece of fridge magnet to the end of the probe.
Seats the pellets better, and retains BB's.
( not that I'd ever recommend shooting BB's through a rifled pellet barrel, mind you )

The .177 bolt will seal the .22 barrel, sorta, with an over-sized "O" ring.
Much better using the .22 bolt for both.


 
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